1. Field of the Invention
The present invention relates to a technology for performing a transparent processing in a data transfer apparatus.
2. Description of the Related Art
Conventionally, a display control apparatus that reads display image data and performs data output to a display panel have been generally known. Such a display control apparatus includes a micro control unit and a memory having stored therein image data, which serves as materials for display image data, final display data, or image data being edited. To allow an image to be displayed on the display panel, the display control apparatus reads the display image data at predetermined timing and outputs data to the display panel. In a display control system having such a display control apparatus connected thereto, when a display image is generated by combining and arranging image data stored in the memory and also a transparent transfer process is required, for the purpose of data transfer, it is effective to use a data transfer apparatus by hardware, rather than read and write of a CPU.
For such a process, a transparent-detection-data transfer control apparatus has been disclosed in Japanese Patent Laid-Open Publication No. 8-63587, in which, when data read from a predetermined address by using a transparent register storing transparent color coincides with a transparent-register set value, the apparatus performs a transparent transfer process with an operation of refraining from transferring that data.
However, in data transfer apparatuses for use in generating image data, not only a transparent function but also a palette conversion function is often required, in which an input color space is converted to another color space by using a Look-Up Table (LUT) for transfer. If a data transfer apparatus supports only a transparent function but not the palette transformation function, such a data transfer apparatus is useless and a transfer operation including the palette transformation process has to be performed by the CPU. This poses a problem of increasing a transfer process time.